Not had one specifically for Admiral, however phone interviews tend to be to see how you speak on the phone. As with most call centres (as that is what this would have been for) you need to be clear on the phone, so by starting with the phone interview (which is usually just a general chat to be honest, talking to you about your CV, really just to hear how you are on the phone) and possibly a couple of general interview questions to see if it is worth calling you in for a more formal interview